Referring to FIG. 9, a gas turbine engine is generally indicated at 110 and comprises, in axial flow series, an air intake 111, a propulsive fan 112, an intermediate pressure compressor 113, a high pressure compressor 114, combustion equipment 115, a high pressure turbine 16, an intermediate pressure turbine 117, a low pressure turbine 118 and an exhaust nozzle 119.
The gas turbine engine 110 works in a conventional manner so that air entering the intake 111 is accelerated by the fan 112 which produce two air flows: a first air flow into the intermediate pressure compressor 113 and a second air flow which provides propulsive thrust. The intermediate pressure compressor 113 compresses the air flow directed into it before delivering that air to the high pressure compressor 114 where further compression takes place.
The compressed air exhausted from the high pressure compressor 114 is directed into the combustion equipment 115 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate and low pressure turbines 116, 117 and 118 respectively before being exhausted through the exhaust nozzle 119 to provide additional propulsive thrust. The high, intermediate and low pressure turbine 116, 117 and 118 respectively drive the high and intermediate pressure compressors 114 and 113, and the fan 112 by suitable interconnecting shafts.
Low pressure fan outlet guide vanes (OGVs) 100 are located behind the propulsive fan 112 in a bypass duct 101 of the gas turbine engine 110. The fan outlet guide vanes 100 have two functions. An aerofoil profile of the fan outlet guide vane 100 straightens air flow through the bypass duct 101 to improve engine efficiency and therefore fuel consumption. The fan outlet guide vanes 100 also act as structural components in order to transmit engine loads to the nacelle and casing of the gas turbine engine 110 and so support that nacelle structure upon the core of the gas turbine engine 110.
Typically, fan outlet guide vanes 100 are manufactured from sheet material for example a titanium alloy such as Ti 6A1 4V. The main structural factor is flutter margin which in turn is related to aerofoil curvature and its maximum chordal thickness.
Previously, fan outlet guide vanes 100 have been manufactured in accordance with a method whereby two plates or a folded plate of material are diffusion bonded along respective abutting edges and then superplastically deformed by inflation to create a hollow structure. In such circumstances, maximum chordal thickness varies in a linear progression along the length of the fan outlet guide vane structure. It will be understood that the diffusion bonded edge portions are relatively stable and not inflated whilst the central sections of the vanes are machined to allow the thin inflation process to form the hollow structure. In such circumstances utilising sheet to sheet flat materials necessitates use of thicker materials at the edges than necessary in order to ensure there is adequate material in the central sections to provide the linear progression in thickness for structural strength. Such additional material adds to weight as well as cost.
In accordance with the present invention there is provided a guide vane for a gas turbine engine, the guide vane comprising a first end, a second end, a first longitudinal edge, a second longitudinal edge and sheet portions, the sheet portions being bonded along the first and second longitudinal edges, the sheet portions being deformed to form a cavity therebetween, the deformed sheet portions defining a non linear variation in maximum chordal thickness along the guide vane between the first end of the guide vane and the second end of the guide vane.
Preferably each sheet portion being convex outwardly between the first and second ends of the guide vane.